The present invention relates to an abnormality detecting apparatus for an intake system of an internal combustion engine, and more particularly to an apparatus for detecting an abnormality of the intake system of the internal combustion engine which has a bypass passage bypassing a throttle valve and an idling control valve for controlling the amount of air supplied through the bypass passage.
There is a known technique of recirculating a blow-by gas that leaks from a combustion chamber of an internal combustion engine into a crankcase, to an intake system for thereby preventing the blow-by gas from being discharged into the atmosphere. Methods for detecting a leak caused by breakage or dislocation of a blow-by gas passage which recirculates a blow-by gas to the intake system are disclosed in Japanese Patent Laid-open No. 10-184335 and Japanese Patent Laid-open No. 10-184336.
Japanese Patent Laid-open No. 10-184335 discloses a method in which an idling control valve disposed in a bypass passage that bypasses a throttle valve is controlled to equalize the idling rotational speed of the engine to a predetermined rotational speed, and it is determined that the blow-by gas passage is abnormal when the opening of the idling control valve is smaller than a predetermined opening, or when an intake pressure detected during idling is higher than a predetermined pressure.
Japanese Patent Laid-open No. 10-184336 discloses a method in which the blow-by gas passage is determined to be abnormal when a pressure detected by a gas pressure sensor disposed in the blow-by gas passage becomes a value which is outside a predetermined range.
The method disclosed in Japanese Patent Laid-open No. 10-184335 determines the abnormality based on the opening of the idling control valve or the intake pressure. In other words, the method does not determine the abnormality by estimating or detecting the amount of intake air supplied to the engine. Therefore, there remains a possibility to improve accuracy of determination.
The method disclosed in Japanese Patent Laid-open No. 10-184336 is not preferable because a gas pressure sensor is additionally required, resulting in a complex configuration and an increased cost.
It is an object of the present invention to provide an abnormality detecting apparatus which is capable of more accurately determining abnormality of the intake system, including abnormality of the blow-by gas passage, with a relatively simple configuration.
According to the present invention, an abnormality detecting apparatus for an intake system of an internal combustion engine, which detects an abnormality of the intake system, is provided. The intake system has a throttle valve, a bypass passage bypassing the throttle valve, and an idling control valve for controlling the amount of air supplied through the bypass passage. The abnormality detecting apparatus comprises a first means, a second means, a third means, and an abnormality determining means. The first means calculates a total intake air amount (QTOTAL) supplied to the engine. The second means calculates an amount of intake air (QBP) supplied through the bypass passage based on a valve opening control quantity for the idling control valve. The third means calculates a parameter (QL) indicative of a leak air amount of the intake system according to the result of a comparison between the total intake air amount (QTOTAL) calculated by the first means and the amount of intake air (QBP) calculated by the second means. The abnormality determining means determines that the intake system is abnormal when the parameter (QL) calculated by the third means is greater than a determination threshold (QTH) in an engine operating condition where the throttle valve is substantially fully closed.
With this configuration, the total intake air amount supplied to the engine is calculated and the amount of intake air supplied through the bypass passage is calculated based on the valve opening control quantity for the idling control valve. Further, the parameter indicative of a leak air amount of the intake system is calculated according to the result of a comparison between the total intake air amount and the amount of intake air supplied through the bypass passage. It is determined that the intake system is abnormal when the parameter calculated by the third means is greater than a determination threshold in the engine operating condition where the throttle valve is substantially fully closed. The parameter indicative of the leak air amount corresponds to the amount of air which is other than the amount of air supplied through the bypass passage and included in the total intake air amount at the time the throttle valve is substantially fully closed. Therefore, by using this parameter, the abnormality of the intake system can be determined accurately without the need for a specific sensor for determining such abnormality.
Preferably, the abnormality determining means sets the determination threshold (QTH) according to a load on the engine (PBG).
With this configuration, the determination threshold is set according to the load on the engine. Accordingly, the abnormality of the intake system can be determined accurately even when the load on the engine changes.
Preferably, the first means includes a fuel supply amount calculating means for calculating a fuel supply amount per unit time (TIxc3x972NE) according to an engine operating condition so that the air-fuel ratio of an air-fuel mixture supplied to the engine becomes constant, and calculates the total intake air amount (QTOTAL) based on the fuel supply amount per unit time.
Preferably, the abnormality detecting apparatus further comprises a voltage sensor for detecting an output voltage (VB) of a battery which supplies electric energy to the idling control valve, and an inhibiting means for inhibiting the abnormality determination by the abnormality determining means when the output voltage (VB) detected by the voltage sensor is lower than a predetermined voltage (VBO).
Preferably, the abnormality detecting apparatus further comprises a first average value calculating means for calculating a first average value (QTAVE) by averaging values of the total intake air amount calculated by the first means, and a second average value calculating means for calculating a second average value (QBPAVE) by averaging values of the amount of intake air calculated by the second means, wherein the third means calculates the parameter (QL) indicative of the leak air amount according to the first and second average values.